The present invention relates to a method and apparatus for controlling the amounts (quantities; volumes; proportions) of components being fed into a continuous, static mixer of the thin layer type. The apparatus directly controls a slit of annular nozzles which convert the component flows into thin layers in a mixing apparatus, so as to be able to control the layer thicknesses and hence the through-put quantity.
Continuous static mixing is generally characterized by components being fed continuously and at a high speed into a mixing apparatus without moving parts, where only the kinetic energy is used for mixing. This is in contrast to a batch mixing process with charge feeding, and where mixing is effected by means of agitators or overturning the compound.
Today, mixing processes are part of almost all process industry. In order to save energy, investments, labor, etc. there is an increasing tendency to avoid batch mixing and turn to a continuous mixing procedure. The present method and control apparatus increases the range of use for thin layer mixing, so that this mixing system will be used increasingly with raw material combinations like: powder/powder, powder/liquid, liquid/liquid and powder or liquid/gas, vapour or air and in special cases: large quantity/small quantity.
In continuous, static thin layer mixing, the mixing process takes place inside a mixing head, where preferably a fluidized powder component or suspension is fed in axially from above, and where a liquid or gas component has a radial inlet. The raw materials are subjected to a moderate excess pressure before being led through off/on valves into the mixing head nozzles, where static pressure is converted to kinetic energy. Thin layers are formed by the axial component out flow of the nozzle when the flow is spread out on an underlying cone surface while thin layers of the radially introduced component are formed in annular nozzles. When the thin layers meet in a freely flowing circular mixing zone, an instantaneous mixing effect is achieved with an instantaneous further transport of the mixed product out of the mixing zone. The best mixing result is achieved in a mixing zone where a downwards directed layer of axially introduced raw material meets one layer from the outside and one layer from the inside, both containing the radially introduced raw material. This means that the radial raw material flow is distributed to an annular nozzle on the outside and an annular nozzle on the inside of the mixing zone.
So far, the thin layer mixing method has not gained any substantial ground. This is due to the fact that this method has not included an effective method and apparatus for adjusting the amount of raw material before the mixing process is started, nor a possibility of being able to adjust the quantities during mixing. With normal pressure/quantity control valves in front of the mixing head, it will certainly be possible to regulate the quantities. However, the exit velocity from the nozzles will then be different with an unchanged nozzle cross section. Besides, the available pressure convertible to velocity in the nozzle will be reduced in the valve system.